Tag Archives: BLS

Some pectus excavatum patients have a metal ‘Nuss bar’ inserted below the sternum which can make chest compressions more difficult. In those without one, standard compression depths compress the left ventricle more than in non-pectus subjects, and might lead to myocardial injury.

This has led to a recommendation in the journal Resuscitation:

“Until further studies are available, we recommend strong chest compressions, according to the current guidelines, in PE patients with a sternal Nuss bar and, to minimize the risk of myocardial injury, we suggest a reduced chest compression depth (approximately 3–4 cm) at the level of lower half of the sternum in PE patients who have not had corrective surgery.“

The recent LINC trial was a randomised controlled trial comparing a mechanical chest compression device (LUCAS) with manual CPR(1). “No significant difference” was found for any of the main outcome measures considered.

So do you think the LINC trial demonstrated that mechanical CPR using the LUCAS device is equivalent, or at least not inferior, to manual CPR?

This was an interesting and important trial for those of us who manage prehospital cardiac arrest patients. In some social media discussions, it appears to have been interpreted by some as evidence that they are equivalent resuscitative techniques or that LUCAS is not inferior to manual CPR.

However, unless you see a p-value less than 0.05 in the table above, (issues of multiple hypotheses testing aside) no evidence of anything was demonstrated; not of difference and certainly not of equivalence. When faced with 2-sided p values >5%, investigators often conclude that there is “no difference” between the treatments, leading to an assumption among readers that the treatments are equivalent. A better conclusion is that there is “no evidence” of a difference between treatments (see opinion piece by Sackett, 2004(2)). In order to determine if treatments are equivalent, equivalence must be tested directly.

How can we test for equivalence?
First, we must define equivalence. It is crucial that this definition is provided a priori i.e. defined before the data are examined. As the focus of the LINC study was on superiority the investigators did not offer an a priori definition of equivalence. However, the CIRC study(3), conducted some time earlier and similar in design, did. (This study examined an alternative mechanical CPR device, the Zoll AutoPulse).

When establishing equivalence between treatments, instead of the more customary null hypothesis of no difference between treatments, the hypothesis that the true difference is equal to a specified ‘delta’ (δ) is tested (4).

To analyse the LINC results to look for equivalence, we can derive our delta values from the CIRC study, which as we’ve said did offer an a priori definition of equivalence. For the purpose of illustration, we will use the risk-difference stopping boundaries calculated for the CIRC study, rather than the odds ratio based equivalence margins, on the grounds of greater simplicity and clinical appropriateness. Therefore, we set our equivalence margins at -δ=-1.4% and δ=1.6%, meaning, where LUCAS fared no worse than manual CPR by 1.4% and no better by 1.6%, we will consider the two techniques equally efficacious. Thus, we will declare equivalence between LUCAS and manual CPR if the 2-sided 95% CI for the treatment difference lies entirely within -1.4% and 1.6%, and noninferiority if the one-sided 97.5% CI for the treatment difference (equivalent to the lower limit of the two-sided 95% CI) lies above -1.4%. (5).

These concepts and how they differ from a traditional comparison are more readily appreciated graphically (Fig. 1).

Figure 1. Two one-sided test procedure and the equivalence margin in equivalence/noninferiority testing between LUCAS and manual CPR

1a Traditional comparative study, such as the LINC trial, shows results with confidence intervals that show no evidence of a difference as they encompass 0.

1b. Using equivalence margins (-δ and δ) derived from a similar study (CIRC), we show that the LINC trial does not demonstrate that LUCAS and manual CPR are equally efficacious, since the 95% CI do not lie completely within the equivalence margins.

1c. The one sided CI lies above -δ for some outcomes, allowing us to declare non-inferiority on those measures.

Conclusion
The presentation of the LINC trial’s results shows no evidence of a difference in outcomes between mechanical and manual CPR, which is not the same as showing they are equivalent or that mechanical CPR is non-inferior. However if we re-examine their data using equivalence margins (-δ, δ) derived from a similar study (CIRC), there is some evidence that the LUCAS device is not inferior to manual CPR (but not necessarily equivalent) with respect to longer term good neurological outcome.

A recent study showed superior effectiveness of one bag-mask ventilation style over another in novice providers. The technique recommended is the thenar eminence grip, in which downward pressure is applied with the thenar eminences while the four fingers of each hand pull the jaw upwards toward the mask.

Interestingly, in their crossover study in which the thenar emininence (TE) technique was compared with the traditionally taught ‘CE’ technique, they demonstrated a ‘sequence effect’. If subjects did TE first, they maintained good tidal volumes when doing CE. However if they did CE first, they achieved poor tidal volumes which were markedly improved when switching to TE.

The authors suggest: “A possible explanation for this sequence effect is that the TE grip is superior. When one used the TE grip first, he or she was more likely to learn how a good tidal volume “feels” and then more likely to apply good technique with the EC grip.“.

Some of us have been practicing and teaching this technique for a while. None have put it better than the brilliant Reuben Strayer of EM Updates in this excellent short video:

STUDY OBJECTIVE: To determine which of two facemask grip techniques for two-person facemask ventilation was more effective in novice clinicians, the traditional E-C clamp (EC) grip or a thenar eminence (TE) technique.

DESIGN: Prospective, randomized, crossover comparison study.

SETTING: Operating room of a university hospital.

SUBJECTS: 60 novice clinicians (medical and paramedic students).

MEASUREMENTS: Subjects were assigned to perform, in a random order, each of the two mask-grip techniques on consenting ASA physical status 1, 2, and 3 patients undergoing elective general anesthesia while the ventilator delivered a fixed 500 mL tidal volume (VT). In a crossover manner, subjects performed each facemask ventilation technique (EC and TE) for one minute (12 breaths/min). The primary outcome was the mean expired VT compared between techniques. As a secondary outcome, we examined mean peak inspiratory pressure (PIP).

MAIN RESULTS: The TE grip provided greater expired VT (379 mL vs 269 mL), with a mean difference of 110 mL (P < 0.0001; 95% CI: 65, 157). Using the EC grip first had an average VT improvement of 200 mL after crossover to the TE grip (95% CI: 134, 267). When the TE grip was used first, mean VTs were greater than for EC by 24 mL (95% CI: -25, 74). When considering only the first 12 breaths delivered (prior to crossover), the TE grip resulted in mean VTs of 339 mL vs 221 mL for the EC grip (P = 0.0128; 95% CI: 26, 209). There was no significant difference in PIP values using the two grips: the TE mean (SD) was 14.2 (7.0) cm H2O, and the EC mean (SD) was 13.5 (9.0) cm H2O (P = 0.49).

CONCLUSIONS: The TE facemask ventilation grip results in improved ventilation over the EC grip in the hands of novice providers.

An interesting animal study examined the techniques recommended in basic choking management algorithms for foreign body airway obstruction (chest and abdominal thrusts). In terms of the pressures generated, lateral chest thrusts were the most effective, although they are not recommended in current guidelines.

The technique described (on intubated pigs) was:

The animals were placed on the floor and on their side. The lower (dependent) side of the chest was braced by the ground and thrust was applied to the upper part of the upper side by two hands side by side with the higher one just below the axilla.

Interestingly – and I didn’t know this (although perhaps should have!) – the Australian Resuscitation Council (ARC) recommended lateral chest thrusts instead of abdominal thrusts for over 20 years.

While we should always exercise extreme caution in extrapolating animal studies to humans, this makes me want to consider lateral thrusts in the first aid (ie. no equipment) situation if other measures are failing.

Objective Anterior chest thrusts (with the subject sitting or standing and thrusts applied to the lower sternum) are recommended by the Australian Resuscitation Council as part of the sequence for clearing upper airway obstruction by a foreign body. Lateral chest thrusts (with the victim lying on their side) are no longer recommended due to a lack of evidence. We compared anterior, lateral chest and abdominal thrusts in the generation of airway pressures using a suitable animal model.

Methods This was a repeated-measures, cross-over, clinical trial of eight anaesthetised, intubated, adult pigs. For each animal, ten trials of each technique were undertaken with the upper airway obstructed. A chest/abdominal pressure transducer, a pneumotachograph and an intra-oesophageal balloon catheter recorded chest/abdominal thrust, expiratory air flows, airway and intrapleural pressures, respectively.

To alleviate aortocaval compression, it is recommended to tilt pregnant patients into the left lateral tilt position during resuscitation. Aortocaval compression may however occur despite a lateral tilt of up to 34°, thought to be due to the relative immobility of the gravid uterus, although tilting beyond 30° is likely to lead them to slide off the bed or stretcher.

It may be more effective to tilt the patient into the full left lateral position first before returning them to the left lateral tilt position.

Positioning the parturient from supine to the left lateral tilt position (supine-to-tilt) may not effectively displace the gravid uterus, but turning from the left lateral position to the left lateral tilt position (left lateral-to-tilt) may keep the gravid uterus displaced and prevent aortocaval compression.

Our results suggest that moving a full-term parturient from the full left lateral to the lateral tilt position may prevent aortocaval compression in full-term parturients more efficiently than when positioning the parturient from a supine to left lateral tilt position.

Effect of positioning from supine and left lateral positions to left lateral tilt on maternal blood ﬂow velocities and waveforms in full-term parturientsAnaesthesia. 2012 Aug;67(8):889-93

A study of nonshockable out of hospital cardiac arrest survival showed significant improvement in short- and long-term survival and neurological outcome after implementation of a protocol consistent with CPR guidelines that prioritised chest compressions. These improvements were especially evident among arrests attributable to a cardiac cause, although there was no evidence of harm among arrests attributable to a noncardiac cause.

This was not a randomised trial so unrecognised factors may have contributed to the improved outcome in addition to the change in CPR protocol. However, it is interesting as it provides up to date survival rates from a large population sample: Non shockable out of hospital cardiac arrests achieve return of spontaneous circulation in 34%, 6.8% are discharged from hospital (5.1% with a favourable neurological outcome), and 4.9% survived one year.

The breakdown between PEA and asystole is of course telling, and unsurprising, with 12.8% versus 1.1% being discharged with a favourable neurological outcome, respectively. I would imagine then that some of the PEA patients had beating hearts with hypotension extreme enough to cause pulselessness (pseudo-electromechanical dissociation) – clinically a ‘cardiac arrest’ but really nothing of the sort, and the reason we use cardiac ultrasound to prognosticate.

BACKGROUND: Out-of-hospital cardiac arrest (OHCA) claims millions of lives worldwide each year. OHCA survival from shockable arrhythmias (ventricular fibrillation/ tachycardia) improved in several communities after implementation of American Heart Association resuscitation guidelines that eliminated “stacked” shocks and emphasized chest compressions. “Nonshockable” rhythms are now the predominant presentation of OHCA; the benefit of such treatments on nonshockable rhythms is uncertain.

CONCLUSION: Outcomes from OHCA resulting from nonshockable rhythms, although poor by comparison with shockable rhythm presentations, improved significantly after implementation of resuscitation guideline changes, suggesting their potential to benefit all presentations of OHCA.

Some defibrillators have accelerometers capable of measuring chest compression depth during CPR. This allowed a study correlating compression depth with survival in out of hospital cardiac arrest.
More than half of patients received less than the 2005 recommended chest compression depth of 38–51 mm and >90% received less than the 2010 recommended depth of >50 mm. There was an inverse relationship between rate and depth, ie. rescuers had a tendency to ‘push hard, push slow’ or ‘push soft, push fast’.

The authors state:We found an association between adequate compression depth and good outcomes but could not demonstrate that the 2010 recommendations are better than those from 2005. Although we believe that compression depth is an important component of CPR and should be measured routinely during cardiac arrest resuscitation, we believe that the optimal depth is currently unknown.

BACKGROUND: The 2010 international guidelines for cardiopulmonary resuscitation recently recommended an increase in the minimum compression depth from 38 to 50 mm, although there are limited human data to support this. We sought to study patterns of cardiopulmonary resuscitation compression depth and their associations with patient outcomes in out-of-hospital cardiac arrest cases treated by the 2005 guideline standards.

MEASUREMENTS: We calculated anterior chest wall depression in millimeters and the period of active cardiopulmonary resuscitation (chest compression fraction) for each minute of cardiopulmonary resuscitation. We controlled for covariates including compression rate and calculated adjusted odds ratios for any return of spontaneous circulation, 1-day survival, and hospital discharge.

CONCLUSIONS: We found suboptimal compression depth in half of patients by 2005 guideline standards and almost all by 2010 standards as well as an inverse association between compression depth and rate. We found a strong association between survival outcomes and increased compression depth but no clear evidence to support or refute the 2010 recommendations of >50 mm. Although compression depth is an important component of cardiopulmonary resuscitation and should be measured routinely, the most effective depth is currently unknown.

Interesting – mouth to nose breathing was more effective than mouth-to-mouth in simulated resuscitations using anaesthetised, apnoeic patients:

BACKGROUND: The authors hypothesized that mouth ventilation by a resuscitator via the nasal route ensures a more patent airway and more effective ventilation than does ventilation via the oral route and therefore would be the optimal manner to ventilate adult patients in emergencies, such as during cardiopulmonary resuscitation. They tested the hypothesis by comparing the effectiveness of mouth-to-nose breathing (MNB) and mouth-to-mouth breathing (MMB) in anesthetized, apneic, adult subjects without muscle paralysis.

METHODS: Twenty subjects under general anesthesia randomly received MMB and MNB with their heads placed first in a neutral position and then an extended position. A single operator performed MNB and MMB at the target breathing rate of 10 breaths/min, inspiratory:expiratory ratio 1:2 and peak inspiratory airway pressure 24 cm H₂O. A plethysmograph was used to measure the amplitude change during MMB and MNB. The inspiratory and expiratory tidal volumes during MMB and MNB were calculated retrospectively using the calibration curve.

An increase in rib fractures was observed at autopsy in infants who had undergone CPR, which is temporally related to the introduction of guidelines stressing the hand-encircling two-thumb method of CPR and compression depths of 1/3 – 1/2 the anteroposterior diameter of the chest, which has been shown in previous studies to produce higher coronary perfusion pressures and more consistently correct depth and force of compression than the “two-finger” technique.

Previous posts here have reported a CT scan-based mathematical modelling study that suggested compressing to 1/3 anteroposterior chest wall diameter should provide a superior ejection fraction to 1/4 depth and should generate less risk for over-compression than 1/2 AP compression depth, and another post described a small case series of 6 PICU patients requiring CPR for cardiac arrest due to primary cardiac disease in which blood pressure as measured by an arterial line increased when the depth of chest compression was increased from one third to one half of the chest wall diameter (using the hand-encircling method).

What should we do about this? I think the take-home message is to be mindful of the risk of rib fractures and to avoid over-compression, but to follow the guidelines. Another valuable point was made by the authors:
“Regardless of the reason for the increased incidence, the possibility of CPR-related rib fractures needs to be seriously considered in the evaluation of any infant presenting with rib fractures, when there is a history of CPR, so as not to misinterpret the finding as evidence of non-accidental/inflicted injury.”

An infant NOT requiring CPR. And a happy doctor.

OBJECTIVE: A recent increase in the number of infants presenting at autopsy with rib fractures associated with cardio-pulmonary resuscitation (CPR) precipitated a study to determine whether such a phenomenon was related to recent revision of paediatric resuscitation guidelines.

METHODS: We conducted a review of autopsy reports from 1997 to 2008 on 571 infants who had CPR performed prior to death.

RESULTS: Analysis of the study population revealed CPR-related rib fractures in 19 infants (3.3%), 14 of whom died in the 2006-2008 period. The difference in annual frequency of CPR-related fractures between the periods before and after revision of paediatric CPR guidelines was statistically highly significant.

CONCLUSIONS: The findings indicate that CPR-associated rib fractures have become more frequent in infants since changes in CPR techniques were introduced in 2005. This has important implications for both clinicians and pathologists in their assessment of rib fractures in this patient population.

A nice idea – using a single adult self-inflating bag for the resuscitation of adult and paediatric patients, marked to identify compression points that deliver specific tidal volume ranges. Might be useful in situations where equipment needs to be minimised, such as military or pre-hospital settings.

AIM: To overcome limitations of inaccurate tidal volume (TV) delivery by conventional selfinflating paediatric and adult bags during paediatric and adolescent resuscitation, we designed a novel target volume marked bag (TVMB) with four compression points marked on an adult bag surface. The aim of this study was to evaluate the TVMB in delivering preset TV.

METHODS: Fifty-three subjects (28 doctors, 17 nurses, 8 paramedics) participated in this simulation trial. TVMB, paediatric bag and adult bag were connected to a gas flow analyser for measuring TV and peak inspiratory pressure (PIP). In a random cross-over setting, participants delivered 10 ventilations using the adult bag, paediatric bag or TVMB in each of four target volume ranges (100-200ml, 200-300ml, 300-400ml, 400-500ml). We compared TV and PIP for the adult bag, paediatric bag and TVMB in each subject.